1. Field of the Invention
This invention relates to devices relying on magnetic properties and, more particularly, those which in operation rely on magnetic properties to support single wall magnetic domains.
2. Art Background
An integral part of any magnetic bubble device is a layer of a material that has magnetic anisotropy which is capable of supporting single wall magnetic domains. One general class of such domain supporting materials has a garnet crystal structure. Thus, the interest in magnetic devices has generated a corresponding interest in garnet materials exhibiting the necessary anisotropy. While, for these materials anisotropy is one very significant property, a material simultaneously yielding the desired anisotropy and the rapid propagation of single wall magnetic domains is even more significant.
To a certain extent, the two desirable properties of high mobility and the requisite anisotropy are mutually exclusive. Growth induced uniaxial anisotropy is generally produced by the introduction of at least two rare earth (rare earth for the purpose of this discussion includes yttrium) ions at least one of which is magnetic, e.g., samarium, in the dodecahedral site of the garnet crystal lattice. To achieve practical growth induced uniaxial anisotropy, i.e., K.sub.u 's greater than 7000 ergs/cm.sup.3 (K.sub.u being defined as the energy expended per unit volume to rotate a magnetic material in a saturating magnetic field from normal to parallel to the field) the use of magnetic rare earth elements has been essential. However, the presence of a magnetic rare earth element in concentrations necessary to produce a desirable level of anisotropy also tends to restrict the mobility of single wall magnetic domains in the garnet material.
The interdependence of magnetic anisotropy and mobility for present garnet materials produces some limitations. Probable advances in fabrication techniques for bubble devices will allow use of smaller and smaller single wall magnetic domains. The exploitation of this new range of domain size is quite desirable since smaller magnetic domains allow the storage of a greater amount of information in a given area of magnetic garnet material. Nevertheless, the stability of small magnetic domains relies on the use of materials having very high K.sub.u 's. As discussed previously, the use of high K.sub.u 's may limit mobility, and in turn limit the speed at which stored data is processed.